#2419 - Sypharochiton sinclairi - Blue-ringed Chiton
AKA Chiton sinclairi.
Chitons are also called coat-of-mail shells, sea cradles or suck-rocks, or more formally as loricates, polyplacophorans, or polyplacophores. The name chiton is Latin derived from the Ancient Greek word khitōn, meaning tunic (which also is the source of the word chitin). The Greek-derived name Polyplacophora, for the Class, means 'many tablet bearing', in reference to the chiton's eight shell plates. These plates, known as butterfly shells once the chiton dies, are surrounded by a fleshy muscular girdle which may be armoured with granules or scales, as here.
The blue-ringed chiton is endemic to the North, South, and Stewart Islands, and also recently recorded from the Chathams. There are at least 900 species worldwide, and a good fossil record dating back to the Cambrian.
Polyplacophorans are grazers on algae and other encrusting organisms, and are well-known for their ability to return to their home position as the tide retreats. It's not clear how they navigate, but it may be related to the magnetite that coats their teeth. If dislodged from the rock (difficult, given their powerful grip) many can curl up for protection.
They have thousands of light sensitive organs scattered over their shells - in some species these have aragonite crystal lens and are true eyes. Surprisingly, these eyes only seem to have evolved in the last 10 million years, making them by far the most recent version of the organ.
Chitons have separate sexes, and fertilization is usually external. Some species brood the eggs within the mantle cavity, and the species Callistochiton viviparus gives birth to live young.
Some species are eaten by humans. Other predators include seagulls, sea stars, crabs, lobsters and fish.
Puritutu Rock, New Plymouth, New Zealand.
